When blue-green algae reproduce quickly and bloom, there are physical signs. The blooms can look like blue or green paint spilled into the water, thick puffy blue or green foams on the surface of the water (scums), or swirling colors beneath the surface of the water. A blue-green algal bloom will coat an object when it is dipped into the water. Long strands of green algae, duckweed, and filamentous macro-algae are sometimes confused with blue-green algal blooms (see photos below). Blue-green algae blooms can also have distinct smells. They can smell grassy or septic, and in some cases the smell can cause nausea. These algal blooms can accumulate near the shoreline of lakes and can move based on wind and wave action in the lake.